Anatomy of Critical State Constitutive Models: Simulating Undrained Failure of K ₀-Consolidated Soils

Different features, such as rotational hardening and nonassociated flow, have been added to the classic modified cam-clay (MCC) model. However, there is little knowledge about their role and importance in simulating in situ soils. This study examined the effects of rotational hardening and associated/nonassociated flow on modeling the undrained shear strength of K₀-consolidated clays. For this purpose, three types of rate-independent models were chosen: MCC, MCC with rotational hardening and associated flow (RAMCC), and MCC with rotational hardening and nonassociated flow (RNMCC). The capabilities of the three models in reproducing the K₀ state were first discussed. Then, by proposing a dummy yield surface to account for the effect of rotational hardening, an analytical solution to predict soil undrained shear strength s_u directly from the K₀ state was established. The predicted s_u values were examined against available T-bar data. Results showed that only RNMCC is able to produce a reasonable match no matter the over stress ratio (OCR) profile, while both MCC and RAMCC show overestimation, which increases with increasing OCR.